A study on the catalytic activity and theoretical modeling of a novel dual acidic mesoporous silica

Abstract

A novel mesoporous silica-functionalized dual Brønsted acidic species has been introduced as an efficient catalyst for solvent-free esterification of fatty acids with ethanol. The structure of the catalyst has been characterized by FT-IR spectroscopy, thermal gravimetric analysis (TGA), TEM and N₂ adsorption–desorption. TGA of catalyst 1 showed no weight loss before 200 °C, indicating a high degree of hydrophobicity of the surface of the mesoporous silica. TEM images and nitrogen adsorption–desorption showed no noticeable changes to the structure of the catalyst before and after acid treatment. pH metric analysis was performed for the catalyst to determine the loading of the acidic sites. The structure of the catalyst was modeled by mimicking the surface of functionalized silica gel in the form of a cage-like cluster. Various conformers from the proposed structures were selected and optimized at the B3LYP/6-311++G** level of calculation. Natural bond orbital (NBO) analysis was performed to investigate the nature of hydrogen bonding of the catalyst in more detail. Based on the data gained from the optimized structures of the catalyst, a mechanism was proposed for the esterification reaction.